The invention relates to couplings in general, and more particularly to improvements in pipe couplings, especially threadless pipe couplings. Still more particularly, the invention relates to improvements in couplings of the type wherein the parts or objects (e.g., two coaxial pipes) which are to be connected to each other are surrounded by a housing for one or more gripping or clamping elements with sharp or sharpened portions serving to penetrate into the surfaces of the respective objects.
It is known to provide a pipe coupling with a composite tubular housing whose internal surface has grooves for gripping members which are caused to engage the adjacent pipes when the housing is assembled to surround the abutting or neighboring end portions of the pipes. In accordance with one presently known proposal, the housing has two internal grooves each of which receives three arcuate gripping members which are spaced apart from each other in the circumferential direction of the housing and are tiltable about axes located in planes including the axis of the housing. The radially innermost portions of the gripping members have sets of teeth which penetrate into the material of the adjacent objects (e.g., pipes) in response to tilting of the gripping members relative to the housing. The gripping members are tilted in response to axial movements of the pipes toward or away from each other, and the extent of such tilting is limited by the surfaces bounding the respective groove. Once a gripping element abuts the adjacent surface in the corresponding groove, it holds the respective pipe against further axial movement relative to the other pipe. A drawback of such couplings is that the pipes can perform relatively large axial movements toward or away from each other before the tiltable gripping members become effective.
In accordance with another prior proposal, the housing of the pipe coupling confines roller-shaped gripping or clamping members which extend in the axial or in the circumferential direction of the pipes and have external surfaces provided with teeth which penetrate into the material of the adjacent pipes. Each gripping member is installed in a discrete recess of the housing which forms part of the coupling. Certain surfaces which bound such discrete recesses serve to limit the extent of movement of the respective roller-shaped gripping members in the axial direction of the pipes; these surfaces extend in the circumferential direction of the housing. A drawback of such pipe couplings is that the assembly of a large number of roller-shaped gripping members with their housing takes up much time and also that the making of a large number of recesses in the internal surface of the housing is a costly operation.
It is further known to provide the housing of a pipe coupling with internal grooves for ring-shaped gripping members having a substantially frustoconical profile. The smaller-diameter portion of each ring-shaped gripping member is formed with axially extending slits to provide a number of laminations which alternate with the slits and overlap each other in the circumferential direction of the respective gripping member. The laminations are supposed to constitute claws which penetrate into the material of the adjacent pipe. When the pipes which are connected to each other by the just described coupling tend to move axially and away from each other, the inclination of the ring-shaped gripping members changes and the gripping members begin to offer a pronounced resistance to separation of the pipes. However, such changes in the inclination of ring-shaped gripping members necessitate the application of a very large force which can be generated in response to a pronounced axial shifting of the pipes away from each other so that the coupling becomes effective with a pronounced delay following the start of axial movement of one of the pipes away from the other pipe and/or vice versa. The claws of the ring-shaped gripping members tend to scrape off some material of the pipes, and the accumulations of the scraped off material are intended to constitute obstructions which ultimately prevent further sliding of the claws along the pipes and cause a change in the orientation of the respective ring-shaped gripping members to thereby terminate the axial movements of the pipes away from each other.
German Offenlegungsschrift No. 34 43 943 of Hurter discloses a pipe coupling wherein the housing includes two identical shells serving to confine a one-piece sealing member having sealing lips. The housing is further formed with internal annular grooves which flank the sealing ring and confine gripping members which are urged against the respective pipes in response to assembly of the housing and tightening of the sealing lips around the pipes by means of bolts and nuts which hold the shells of the housing against pivotal movement away from each other. The gripping members are tiltable in their grooves in response to axial movements of the pipes relative to each other. Each gripping member is a laminar body which is made of steel.
U.S. Pat. No. 2,459,251 to Stillwagon discloses a threadless pipe coupling which is similar to the pipe coupling of Hurter except that the ring-shaped sealing element is flanked by two sets of tiltable gripping members in the form of arcuate plate-like dogs.
U.S. Pat. No. 2,225,208 to Crickmer discloses a pipe coupling wherein an elastic packing ring is flanked by two gripping members each of which includes a substantially cylindrical portion and a radially inwardly bent flange capable of penetrating into the material of the adjacent pipe when the pipes tend to move axially and away from each other.
U.S. Pat. No. 4,438,954 to Hattori discloses a pipe coupling with two concavo-convex split ring-shaped gripping members which have a certain freedom of axial movement in the respective internal annular grooves of the housing. The gripping members have pairs of sharp edges which are supposed to penetrate into the peripheral surfaces of the respective pipes in response to axial movement of the pipes relative to each other.